Neonatal jaundice is one of the most common physiological manifestations in newborns; the illness presents itself in nearly 60% of term neonates and in 80% of preterm neonates. The illness is a primary reason for high re-admission rates because of its delayed onset. Jaundice is generally benign as its part of the physiological evolution process of neonate's hepatic system, but incorrect or delayed diagnosis can lead to severe brain damage, causing cerebral palsy or kernicterus. Accurate estimation of jaundice is essential for proper intervention and to prevent the development of jaundice into severe hyperbilirubinemia, especially with a growing number of babies being discharged early and sent home.
In the body, because of the large number of potentially reactive groups in bilirubin, very little bilirubin exists free in circulation. Most of these derivatives rapidly associate with albumin, through a network of reversible hydrogen bonds. Together, free- and albumin-bound bilirubin are referred to as unconjugated bilirubin also known as α-bilirubin. Unconjugated bilirubin on reaching the liver, is covalently conjugated to glucuronic acid forming mono and diglucuronides (β and γ bilirubin) not bound to albumin, collectively known as conjugated bilirubin. The water-soluble bilirubin glucuronides are excreted through feces and urine, while a portion gets reabsorbed in duodenum contributing to the enterohepatic circulation. Note, irreversible binding can also occur, and it is now known that in some jaundiced patients' conjugated bilirubin is present in the serum covalently bound to albumin. This species has been called δ-bilirubin.
Free bilirubin (unconjugated and unbound to albumin) is the suspected as being the only form in which bilirubin can cross the intact blood-brain barrier. In clinical practice, the concentration of total bilirubin in neonates is usually equal to unconjugated bilirubin. Total bilirubin is used as an easily measured proxy for the concentration of unconjugated bilirubin, and hence the risk of bilirubin induced neurotoxicity (BIND) or kernicterus. Although, excess levels of conjugated bilirubin and δ-bilirubin can cause conjugated hyperbilirubinemia and cholestatic jaundice, respectively, it's extremely rare in neonates. Unconjugated hyperbilirubinemia is more common condition as it is a consequence of physiological development of the hepatic system.
Preventing newborns from toxic bilirubin levels has been one of the prime concerns for pediatricians. Currently tools like a nomogram, used for plotting hour specific total serum bilirubin levels vs. age of newborns, are employed to understand the trend of the blood bilirubin levels and potential risk of developing hyper-bilirubinemia prior to discharge. Bhutani's nomogram is the industry standard and has been recommended by both AAP and NICE for the same purpose.
In current practice, using isolated risk factors as a measure to predict the subsequent development of hyperbilirubinemia in early discharged newborns has been largely unsuccessful. On top of that, transcutaneous bilirubin (TcB) measurement, used for screening neonates and preferred for their noninvasiveness, can be confounded by the discrepancies between total serum bilirubin (TB) and TcB values above 12 mg/dL (205 mol/L), resulting in TcB nomograms that underestimate TB levels >12 mg/dL (205 mol/L). Despite the numerous studies to improve jaundice diagnosis in the past 30 years, there has been a relapse in readmissions, bilirubin encephalopathy, and kernicterus. These trends point towards the need, more than ever before, for improved diagnostic methods, and to treat physiological conditions safely and comfortably in home and hospital settings.
In the current liability-focused environment, hospitals have started adapting cost containment strategies, such as managed care, resulting in a continued trend toward a shorter length of stay for patients. Early discharge has had a potential effect on the efficacy of neonatal screening causing increased readmissions due to jaundice. Patient and provider convenience is a contributing factor to the increasing rate of late-preterm delivery.
Prompt and accurate estimation of bilirubin levels can help offset the damage caused by readmission, but the laboratory techniques used in hospitals have several deficiencies, listed below, that prevent them properly managing the complications in neonates, especially jaundice.
A large contribution to error in any test results comes from pre-analytical errors and bilirubin tests are more sensitive: When a sample is drawn there is no continued metabolism that will cause a change in the bilirubin concentration. However, it is well known that bilirubin in a sample can be degraded by exposure to light, which is also used as treatment of hyperbilirubinemia. Irradiation of a serum sample changes the structure of the bilirubin molecule into several different polar (water-soluble) photoproducts. Some studies have shown that in vitro bilirubin may be degraded up to as much as 50% by light degradation. Additionally, the sampling site for bilirubin testing can result in further discrepancies. Even though there is no agreement in the literature as to whether there is any difference in relation to the choice of sampling site, capillary sampling is preferred as it ensures that only small sample volumes are obtained to avoid iatrogenic anemia, but it also introduces additional pre-analytical factors.
One study reports that out of all the participating laboratories, over 60% of laboratories are using the diazo diagnostic methods. The diazo methods come with numerous drawbacks, many of which stem from the interference caused by other proteins present in the heme during direct spectroscopic measurement as well as the pH dependency. Further, the reagents used with these methods can be troublesome to work with, often having poor stability and requiring several volume transfers, which may lead to inaccurate results. Additionally, the methods can be relatively slow, often requiring 30 minutes or more to provide the total serum bilirubin measurement after initiation.
Other less popular methods include enzymatic methods, HPLC, and direct spectroscopy, and each come with unique drawbacks. For example, enzymatic methods often use bilirubin oxidase which is hard to immobilize, unstable, and rather expensive. Regarding HPLC, traditional methods use an assay setup that is expensive, bulky, and complex. Direct spectroscopy methods often require dilutions in order to correct for interference from hemoglobin, carotenoids, and turbidity. Additionally, direct spectroscopy cannot be automated and consequently is limited in clinical application. With the above technologies, the measurement apparatuses are difficult to minimize which has limited their abilities to provide point-of-care (POCT) testing for bilirubin.
The initiation of jaundice treatment depends on the bilirubin levels, which in previous laboratory tests, has required significant levels of blood, has the risk of sample compromise, labor intensive, and time consuming. Although, jaundice is benign, as its part of the physiological evolution process of neonate's hepatic system, incorrect or delayed diagnosis could lead to severe brain damage like cerebral palsy or kernicterus.
Operational inefficiencies in current clinical systems heavily revolve around administrational activities in patient management. Progressive steps towards tackling the situation can be addressed by embracing new technology in order to overcome pain points that include lack of efficiency, avoidable admissions and readmissions, medical errors, defensive practice, communication, and excessive administrative services. Point of care technology is one of the many technological advances that has the potential to reduce operational inefficiencies, improve the patient monitoring, and diagnostic accuracy. This is especially true in the case of neonatal jaundice, where prompt management is essential to prevent disorders such as neurological induced dysfunction (BIND) and kernicterus.
In short, total serum bilirubin is an important clinical measurement in hepatobiliary disorders and haematological disorders; the importance of bilirubin is underlined by the numerous efforts to measure in a clinical setting including spectrophotometry, HPLC, fluorometry, and enzymatic methods. As noted above, these methods have several disadvantages such as excessive sample preparation, time-consuming analyses, interferences, and instability of reagents. Furthermore, these methods need to be performed with consideration of the photosensitivity of the bilirubin which can critically underestimate bilirubin levels if not sampled in the absence of light.